The development of metalworking machines was one of the key factors in the Industrial Revolution that began around the turn of the nineteenth century. This was a class of machine that could make almost anything, including reproducing itself. Researchers in manufacturing processes soon realized that more efficient metalworking machines would reduce the manufacturing cost of whatever products were being made. Thus, great effort was devoted toward understand the various metalworking processes, to increase metal cutting rates, and the like. Better cutting tools were developed. More powerful metalworking machines were developed. Manufacturing engineers came to realize that the most efficient metal cutting operations were those in which the cutting tools were worn out in a surprisingly short time; cutting tools became expendable items in the costs of a manufacturing operation.
As a result of the considerable research devoted to metal cutting operations, the time required for such operations was steadily reduced. While further efforts in this direction will undoubtedly reduce manufacturing time, one can ponder whether the point of diminishing returns has been reached. Researchers in manufacturing engineering began to address this matter many years ago. One researcher found that metal cutting accounted for less than 20% of the time that a part spent in a manufacturing plant. Most of the remaining time was spent awaiting the next manufacturing operation. This realization led to development of dedicated tooling that would be used for the manufacture of just one type of part, but with a reduced time for changing workpieces. It also led to more sophisticated plant layouts, so that the parts flowed through a factory in a logical fashion. Cellular manufacturing was developed. Under this concept, several different manufacturing machines, together with necessary accessory equipment, were clustered in one area of a factory. Thus, a batch of parts could go from incoming raw material to virtually complete parts with few, if any, excursions to other locations where manufacturing operations were performed. Time required for shipping a batch of parts around the plant was significantly reduced. Time spent trying to find parts that had been lost during intra-factory shipment was also reduced.
Managers of manufacturing enterprises began to keep track of work in progress, and to recognize the substantial investment that work in progress represents. Such efforts led to decreasing the number of components kept in inventory for subsequent manufacturing or assembly operations, and to decreasing the inventories of finished products awaiting shipment. The favored size for batches of parts became smaller. While such trends represent reduction in overall costs of manufacturing, such trends also placed pressure on manufacturing operations to change tooling between different manufacturing processes more quickly. The combination of smaller batch size and more widespread use of manufacturing cells has accentuated the need for reducing the time required for changeover of tooling.
Metalworking frequently involves precision machining of workpieces, often within tolerances of a few mils. (One mil is 0.001 inch, or 25 micrometers.) One of the essential prerequisites of precision machining is rigid support of the workpiece. In conventional metalworking practice, dedicated tooling to hold a particular workpiece for the metalworking operation is provided. Such dedicated tooling must provide rigid support for the workpiece.
A metalworking operation can involve the machining of families of workpieces of the same general, proportional shape, but different in size and dimensions. Typically, a family of dedicated holding devices is required for a family of workpiece members. While some parts in a workpiece family can be very small, and the associated dedicated tooling can be manipulated and carried by hand, other workpieces and their dedicated tooling can be much larger, requiring mechanical assistance (e.g., a crane) to lift, carry and position the dedicated tooling devices.
Dedicated tooling is designed to hold one workpiece family member in a precise location and position for the metalworking operation. The alignment of the dedicated tooling and the workpiece it holds to the metalworking machine must be exact, and often requires significant setup time to ensure proper alignment with the metalworking machine. Achieving such alignment is a trial-and-error process, generally requiring repeated steps of tapping the tooling to move it a small distance, tightening the bolts used to secure it in place, and then checking the alignment using dial indicators or the like. The critical nature of this process typically requires attention by the most highly skilled workers in the manufacturing facility. Often, trial parts of the workpiece must be test worked, with minute adjustments of the dedicated tooling to the worktable, to ensure the metalworking operation machines the workpiece properly.
When a metalworking facility needs to machine a variety of members of a workpiece family, there can be significant amounts of production time lost in tooling changeover, in disassembling tooling used on the first workpiece, retrieving the dedicated tooling for the next workpiece, and then installing and aligning the retrieved dedicated tooling, etc. Changing the tooling from that required for one workpiece to that required for another similar workpiece is frequently a major factor in the cost for operating a metalworking facility, particularly when business conditions in the industry can necessitate small production lot sizes.
In addition, to machine a family of workpieces that are similar in size but different in detail, equivalent families of dedicated tooling must be manufactured. Because each set of dedicated tooling must accept and secure the workpiece in generally two or more places for proper positioning and alignment, these dedicated tools can be complex and expensive.
Considerable savings in manufacturing costs can be achieved by simplifying the tooling changeover process. Where a plurality of metalworking machines is used in a manufacturing cell, the need to simplify the tooling changeover process is even greater. During a tooling changeover, it is necessary to change the tooling for each metalworking machine, but in addition, all other machines in the cell are typically idle while the tooling on any one machine is being changed.
The issues discussed hereinabove are well known to those skilled in the metalworking arts and in manufacturing engineering, and are described in Manufacturing Engineering and Technology (Fourth Edition), by Serope Kalpakjian and Steven R. Schmid.
A conventional manufacturing cell 1 is shown in its general configuration in FIG. 1. The manufacturing cell has two numerically controlled machining centers, shown at 2 and 3, inspection equipment, shown at 4, a robot for manipulating workpieces, shown at 5 and a control system, shown at 6. Metalworking machines identified as machining centers typically possess the functional attributes of a milling machine, in that a workpiece is moved past a rotating cutting tool, and additionally possess attributes particularly suited to automation, such as numerical control (N/C), a plurality of cutting tools housed in a magazine, and N/C means for changing cutting tools. A manufacturing cell can contain many different types of metalworking machines, and that there is no theoretical limit to the number of metalworking machines and accessories that can be included in a manufacturing cell.
A conventional milling machine 2 is illustrated in FIG. 2. The typical components of the milling machine are: base 11, column 12, head 13, knee 14, saddle 15, table 8, spindle 16 and cutting tool 17. The customary reference axes that define directions of movement and/or measurement are also shown in FIG. 2. Both the manufacturing cell shown in FIG. 1 and the milling machine shown in FIG. 2 are known to persons skilled in the art. The selection of milling operations for the manufacturing cell shown in FIG. 1 and the metalworking machine shown in FIG. 2 was made solely for illustrating the present invention, and the selection should not be regarded as a limitation on the scope of the present invention.
Milling machines typically have a tooling means for securing the workpiece to the table (not shown in FIG. 2). The various types of conventional tooling for securing the workpiece to the table typically do not provide rapid changeover from one workpiece to the next. Conventional tooling can require substantial disassembly of the tooling to make such a changeover, and substantial time to change the tooling from that used with one member of a family of workpieces to that used with another family member. Each of these factors typically leads to extensive commitment of time by highly skilled technicians to secure the next workpiece, or the next set of tooling, to the table. Whenever a metalworking machine is idled to change either a workpiece or tooling, it cannot perform its intended metalworking function. In the context of a manufacturing cell, where idling any one metalworking machine in the cell can idle other such machines in the cell, these deficiencies are particularly important. The present invention addresses these deficiencies, particularly with respect to manufacturing cells.